Refractory lined ladles are used in the production of ferrous and nonferrous metals to receive the molten metal during and after the various refining stages. These ladles are recycled and normally require preheating of the refractory lining between uses. In addition, new linings require drying as do linings which have been repaired through patching.
The placing of a burner head in a ladle, while simple, has proven to be inefficient and energy wasteful. As a result, cold air and hot air preheat stations have been employed. In a cold air ladle preheat station a ladle is juxtapositioned with respect to a refractory lined burner wall and a burner is fired through the wall into the ladle interior. Hot air preheat stations generally employ some type of hooded arrangement about the burner wall and a portion of the ladle so that the products of combustion are retained and utilized in a recuperator to preheat combustion air for the burner. In both types of preheat stations there is a need to eliminate or minimize the cold air infiltration which takes place between the firing wall and the ladle. Positioning the ladle against the wall so as to form a seal therebetween is difficult to achieve because the lip of the ladle is normally covered with solidified chunks of metal and other types of slag which disrupt the seal and/or cause damage to the sealing surface on the ladle heating apparatus.
In addition to the cold air infiltration between the firing wall and the ladle, radiation heat losses occur as the heat is radiated through the space between the ladle lip and the wall.
Air curtains in general are known and have been used in heat treating furnaces to prevent air losses. One such system is disclosed in U.S. Pat. No. 3,397,874 wherein an air curtain is used in connection with a cover for a soaking pit.
Forced air has been utilized in connection with a tundish cleaning and preheating apparatus as shown in U.S. Pat. No. 3,491,988. In this patent the forced air is utilized to divert flame and to protect the ladle tipping mechanism from the preheating unit.
An annular air screen has also been employed to form a vertical closed chamber for conveying smoke leaving a furnace to a hood located above the furnace. This is illustrated in U.S. Pat. No. 3,834,293.